I had just
finished writing my third and final essay on Symmetry (please see the preceding
blog) and mailed it to THE HINDU, when the newspaper published a
forceful argument by an eminent scientist in response to the first
two essays, asserting that symmetry is not a characteristic feature of
life.
The
author, Dr. D. Balasubramanian, and I were old friends. He was
a Deputy Director of the Center for Cellular & Molecular Biology in
Hyderabad -- a constituent unit of the Council of Scientific &
Industrial Research in New Delhi -- when CCMB was physically and
technically being built in the 1980s ; and as CSIR's friendly
Financial Adviser, I was a discerning source of constant financial and moral
support. He was (and still is!) writing regularly in the
Science & Technology section of THE HINDU, and had won the UNESCO's Kalinga
prize for popularization of science in 1997.
Finding it
difficult to pronounce his name? Try Baala-Subra-Manyan ('u' as in 'put') -- there you are!
Or just call him Bala, as his friends do!
Glossary &
annotations
(in same order as in text)
(in same order as in text)
New Delhi -- Capital of India.
Thermodynamics -- Science exploring relationship between heat and other forms of energy.
Nutrinos -- Sub-atomic particles similar to electrons but having no electrical charge, with extremely small mass.
Macroscopic -- Visible to naked eye (among other meanings).
Beta ray -- An energetic sub-atomic particle.
Molecule -- Minute basic
component of matter, consisting of two or more chemically bonded atoms.
Valency -- Number of bonds which a given element's atoms can form.Amino acids -- Biologically significant chemical compounds, generally containing carbon, oxygen, hydrogen and nitrogen,
Chirality (pronounced 'kairality') -- Preference of matter for asymmetry.
Polymeric -- Pertaining to chemical compound with large molecules made of similar smaller molecules.
DNA (Deoxyribo-nucleic acid) -- A macro-molecule encoding genetic characteristics of life forms.
Deoxiribose -- a deoxy sugar (in which a hydrogen atom replaces a hydroxyl group -- never mind what that means!).
Double helix -- Twin-stranded molecular structure of nucleic acids.
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THE HINDU
Science, Technology, Engineering
25 December 1991
Lack of symmetry and life
"If one took a careful look at things one would realize that symmetry exists on a wide scale in nature, science, art and other concerns of civilized life." So writes Mr. M.V. Ramakrishnan in his two-part 'Articulations' article in The Hindu Sunday Magazine of November 17 and December 1, 1991.
Interesting as it is, this reflection unconsciously highlights but one analytical mode of the human mind. This mode uses patterns and symmetry as bases for analysis, and naturally finds them in many things that it perceives and analyzes. A case of what you seek, or "I think, therefore it is" -- or Cogito ergo est, to paraphrase the famous remark of the 16th-century French philosopher-scientist Rene Descartes, who said Cogito ergo sum or "I think, therefore I am."
Powerful role
The tendency of the human mind to recognize patterns and deduce order within them cannot be gainsaid. Symmetry plays such an extremely powerful role in such analysis that the mind actually 'fills in.' The accompanying picture shows four black discs with bites taken out of them. The four incomplete discs are placed symmetrically in a shaded background. The background prompts the brain to fill in the outline and leads one into perceiving the illusory circle as if it is actually drawn.
Professor V.S. Ramachandran of the University of California at San Diego has been working on this aspect of the brain which is best termed as visual psychophysics. The key point is the psycho part in the term, as he shows that it is the mind that does the filling in, to aid pattern recognition. Showing such pictures at a recent lecture at the Center for Cellular and Molecular Biology, Hyderabad, Prof. Ramachandran wondered if a computer would do such 'filling in' -- or even whether other animals would do so, or would they perceive the pattens as incomplete sketches. "Cogito, ergo est" or "Cogito, ergo sum"?
Chaos in entropy
It is actually rather uncomfortable for the human mind to discover that nature does not necessarily prefer symmetry or order. In fact, some of the more important facets of nature and natural laws seem to underscore the lack of order and symmetry. The concept of entropy, borrowed from thermodynamics and applicable to even societal processes, is one such. Denoting disorder, randomization and dissipation of energy, it is indicative of the downhill trend that is built into natural processes.
Nicolas Leonard Sadi Carnot (1796-1832), a French physicist and pioneer in the study of the efficiency of steam engines, showed that no engine can ever be 100 per cent efficient. There will always be a loss due to friction and other dissipative pocesses. This discovery was soon found to be not so recondite after all, but applicable to any situation where energy is exchanged or transformed. It paved the way for the realization that nothing can come out of nothing, and that it is not possible to ever build a perpetual-motion machine that operates efficiently forever. With time, the system will tend towards losing order and gaining entropy.
Time's arrow
Hence the pithy statement that entropy is time's arrow. It is as if the clock of time unwinds. One cannot wind back this clock of an isolated system. One cannot win, and what is worse, also break even. Friction, dissipation and entropy take care of that. The universe itself, being isolated from anything else, unwinds towards dissipation and greater entropy. It is isolated by definition -- since if there is anything else, that would be included as part of the universe.
Time is thus the direction in which the order or the system decreases or the entropy increases. There is therefore no inherent symmetry in the natural history of the universe itself.
The remarkable point about thermodynamic laws is that they are applicable to all systems -- from a collection of neutrinos in an ensemble of human populations to the universe itself. Whether the universe began with a big bang of primal matter/energy at the start of time and flows downhill since, or whether it is a steady state of cycles . . . it is an one-way street that goes towards greater entropy or disorder. No symmetry here, in the largest possible perspective. The second law of thermodynamics dictates it in the macroscopic world.
When man analyzes the nature and behavior of matter, he looks for pattern, repetition, symmetry, correspondence and connections between parameters that he uses in the analysis. Some of the more important parameters concern the position (the co-ordinates) of the object of study , its motion, electric charge, magnetism, and so on.
In the description of sub-atomic particles, one particularly interesting parameter concerns the symmetry properties of these particles. For quite some time, a major rule concerning the behavior of sub-atomic particles was that it has an in-built symmetry. This is termed conservation of parity, where parity refers to a type of symmetry analogous to that which exists between the left and the right hands.
About 40 years ago, however, Professor (Mrs.) Wu of New York found indications in certain experiments involving the release of beta rays, that parity was not conserved. The system and the experimental set-up themselves were symmetric, with no bias towards one-handedness or the other, yet the stream of beta rays corkscrewing their way out of the system showed a bias towards one-handedness over the other.
'Weak interactions'
Now, one of the four basic forces of nature is the so-called 'weak interactions', which is manifested in the Wu experiments. The observation that parity is not maintained in these interactions therefore leads to the important but unsettling conclusion that nature may inherently display asymmetric behavior. Subsequent to this, two other American scientists also of Chinese origin, C.N. Yang and T.D. Lee, confirmed the property and provided the theoretical perspective, for which they received the Nobel prize in Physics.
An even more remarkable manifestation of nature's asymmetric tendencies occurs in the living world. All living beings are made of molecules, and in particular carbon-containing ones. The carbon atom has a valency of four, and these four arms of the atom are flung out in space, making the molecule three-dimensional and thus analyzable in terms of symmetry operations.
One of the most notable findings in chemistry is that molecules can be right-handed or left-handed in shape. Generally the two forms occur in equal amounts, have the same properties, and can be distinguished from the way they interact with polarized light (such as the one coming through plastic sun-glasses).
Pasteur's finding
A momentous discovery was made a century ago by Louis Pasteur, who showed that microbes contain sugar molecules that are preferentially right-handed and amino acids which are left-handed. He asserted that all life forms are to be recognized through their ability to prefer and enrich molecules of one-handedness or chirality over the other.
In contrast, the inorganic world is symmetric and abounds in materials and molecules where both right-handed and left-handed forms occur in exactly equal amounts. In othe rwords, the distinct signature of life is the presence of asymmetrical molecules which go to make it.
Two-stranded pigtail
What Pasteur found as life's signature has been borne out by molecular biology. All living systems on earth contain polymeric DNA as the master molecule which controls heredity and metabolic events in the cells. And the DNA in all cells is made exclusively of the right-handed form of the sugar deoxyribose.
On top of this asymmetry, the long molecular chain of DNA winds upon itself in the form of a pigtail with two strands, or as a spiral staircase, as a double helix, with the winding in the right-handed mode rather than the other way. This leads to the further feature of dissymmetry which is defined with respect to a mirror-like plane of reflection.
Asymmetry is defined with respect to inversion at a center or point. Inorganic substances in general are not asymmetric but can occasionally be organized in a dissymmetric way. A typical example is quartz which is a form of silica and by itself symmetric. When organized as a crystal, the individual silica units can be put up dissymmetrically as a right-handed spiral or as its mirror image, a left-handed helical arrangement.
When the crystal is dissolved and the single silica molecules are obtained, the
handedness is lost and the system is symmetric again. On the other hand,
when a molecule of life such as DNA is broken down, the dissemmetry is gone but
the resultant deoxyribose is still asymmetrical.
Symmetry in death?
Handedness or chirality is such a manifest feature of life that one can actually detect sneaking small amounts of molecules of the wrong handedness (right-handed amino acids or left-handed sugars) in tissues that are ageing or dead, such as the eye lens or the tooth enamel. Death is characterized by the inability of the system to handle or enrich asymmetric molecules preferentially. This feature is so vital in life and death that it is exploited in the search for extra-terrestrial life.
Samples from the Moon and Mars have been analyzed, as also organic matter from meteorites that have fallen on earth from space. To date, none of the extra-terrestrial organic matter has shown any preferential enrichment of asymmetrical molecules. Based on this, it can be tentatively inferred that as of now, there is no life detected in outer space. From microbes to Martian matter is a unified theme : where there is symmetry there is no active, pulsating life.
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PostScript, 2018
Check and counter-check
When I read Dr.
Bala's article, I felt like sitting in front of a chess board and facing
a formidable champion! With the asymmetrical leaps and bounds of his
twin knights he had certainly pushed my king into a tight corner ;
but with the smooth movements of my linguistic rooks and queen, I mounted a
strong counter-attack. I have no idea whether either of us could have won
the game : I was quite happy to call it a draw!
(Next : A question of Science vs. semantics)
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